Good afternoon,
I have been experiencing serious electric issues since over a year but I did not have to use this car much so it wasn't my priority.
Now, I would like to enjoy it but it is giving me serious / random / intermittent electric issues.
After a lot of digging, I have come to the conclusion that I have either a faulty module that blocks the whole system, or a communication issue directly on the CAN bus.
I have changed ISM, main and auxiliary batteries.
I have checked all fuse and relays (removed, tested and placed back).
When the issue is not present, the diagnostic toold doesn't read any critical fault that would lead to the repeating problem. Car starts without issue and all organs seems to be working.
When it happens, the only way to get out off the limb mode is to disconnect the battery. If a gear is already engaged, it will still drive but not turning signal, no wipers..., rough gear changes and only forward (no change allowed).
The issue has been appearing more frequently lately.
Worth noting that I have check and have not found any trace of water under the driver and passenger foot, nor below the spare wheel (I live in KSA and rain is pretty rare here...)
I haven't found any signs of corrosion wether on the electronic boards nor in the coneectors in those area neither.
I want to attach below 2 OBD-II reports:
- 1st with the car working fine and showing no major DTC
- 2nd one, 5 minutes later, after having all the dash lights on and blinking, showing no more communication with the main engine and drivetrain modules...
Has any of you experienced such issue ?
Any ideas ?
Next step would be to measure hi-CAN bus abd low-CAN bus voltages to try to find a faulty moduel somewhere but I am not extremely confident with this procedure...

Thank you in advance

Starting point as I'm sure you know should be voltage and health of batteries and alternator. They're all good? Absolute Minimum 11.7v engine off and 13.7v engine on. Does that change between the 2 situations you've presented?

Hi BlackML550,
Thank you for your answer.
I did check my batteries.
I have 12,4 V off and 14,15 on.
I believe it is fine.
Both batteries are new.
Alternator is not buy I believe it is doing its job.
Let me know.
Thanks

By any chance were you able to measure voltage (in the same format as above) whilst the problems were present?

Exactly the same.
It doesn't affect the voltage...
As I said, I have ruled out all logical issues (or at least logical to me...)
Now, IMHO, it is due to a communication issue on 1 of the Can-bus, coming either from a faulty module or the can-bus material itself...
I need advise as to how to test this.
Thanks

​

If STAR can point to a specific module, disconnect that module from the system and see if the voltages on the CAN bus stabilize.
In my car, all STAR could indicate was a failure on the CANbus. I ended up verifying voltages on the CAN-Hi and CAN-Lo lines and disconnecting/reconnecting modules one at a time until the system stabilized. Turned out to be a module that STAR did not identify as bad.
See the following link to a post for an idea of what it took on a simpler CANbus. Nonetheless, the CANbus in your vehicle is just a larger and slightly more complicated version. Easier to diagnose than one would think.

https://mbworld.org/forums/e-class-w...is-repair.html

Also see the attached tech document to give you some ideas about troubleshooting the CANbus.

FWIW, I once spent a bit of time outside of Hafr al-Batin. Cold, hot, wet, dry, and desolate yet there were times it was quite beautiful in the spring...

Thank you so much for your detailed answer.
This is exactly what I am expecting.
I will try to follow this path tomorrow and revert back asap.

Hafr Al-Batin, that's a remote place...
Haven't been yet.

Thanks and regards

Any update? did you find your issue? I am experiencing the same issue you have described

2008 W251 here: Had once CAN went crazy. Car essentially stopped. Main radiator fan at full blast, engine sneezes and stops, tonnes of other weird problems. Died on the road, unexpectedly, was flawless and reliable just before that.

Turns out water in the trunk!! Spare tire was flooded. Driving bumpy or turning hard was flooding rear SAM and cables. Judging by the symptoms - definitely CAN, no way it is local to rear SAM.
Cleaned and dried everything - problem went away.
Started to monitor water in the trunk and noticed that after heavy rain spare tire compartment collecting some water. I believe gutters clogged but even today still not able to find exact problem.

I eventually pulled drain rubber plug from floor pan under the spare tire. and now 3 years later never seeing this problem again, everything including floor is dry.